Helically wound tubes are used in a variety of applications. This invention applies particularly to a filter center tube used in an oil filter for an automobile. Many of these tubes are made of paper sheet material which provides a low cost filter center tube that can be discarded and economically replaced. One problem encountered is how to economically manufacture a helically wound tube with perforations that provide adequate radial flow.
Some current tubes are made of multiple plies of material that are helically wound, trimmed to size, and then perforated. This is an expensive manufacturing process. Another type of filter center tube, as disclosed in U.S. Pat. No. 2,354,481 issued 25 Jul. 1944 to J. K. Russell may use one preperforated sheet that is spirally wound about itself to form a multiple layered tube. A disadvantage of this tube is that a ridged axial edge is formed where the sheet ends. The ridged edge provides an unsmooth outer layer that may wear against the filtering material that encloses the tube.